The present invention relates generally to video cameras, and more particularly to zoom indicating apparatus for use with such cameras and similar optical systems.
Video cameras, such as television broadcast cameras, which employ zoom lenses that allow the camera operator to vary the focal length, and thus the field of view of the camera, present problems for the operator. The operator must be able to determine the current focal length of the lens, in order to determine how much zoom range is left. Although most lenses are marked to indicate their focal length setting, the operator is usually unable to see the markings from his normal operating position. With cameras that have remote zoom control, an electrical signal related to the zoom setting of the lens is available from the zoom control servo system. In the past, this signal has been applied to meters, calibrated in either percentage of maximum zoom range or directly in focal length and arranged to be easily viewed from the operator's position; or the signal has been used to display zoom setting information in the viewfinder of the camera outside of the normal field of view presentation, as by a representation of a meter needle or a line having a length proportional to the zoom setting.
Although past arrangements have provided convenient access to zoom setting information, the operator is still required to perform a difficult interpretation of the displayed information. He must determine the zoom range remaining from the current setting, and then must attempt to visualize the field of view that would be covered if the camera were zoomed in to its maximum setting. A complicating factor is that it is practically impossible to precisely align the optical axis of the lens with the center of the image scanned on a camera sensor tube. Misalignment between the optical axis of the lens and the scanned image causes objects to appear to move with respect to the center of the picture as the lens is zoomed in and out. Thus, it is difficult to estimate precisely the portion of a scene that would be within the field of view of the camera at different zoom settings.